[PSUBS-MAILIST] Optical Oxygen Sensors

Thu Aug 8 09:05:07 EDT 2019

 Alan, you have a few options.
You can run Processing language on the Raspberry.  The Arduino IDE language is in fact the processing language.  Check out processing.org.  However, you are correct in that the Raspberry is somewhat lacking in communication IO pins and does not have any onboard IO ADC pins.  You can get around the IO limitation by using a multiplexer like https://www.sparkfun.com/products/13906 or https://www.sparkfun.com/products/9056.  You can get around the ADC issue by using an external ADC like https://www.adafruit.com/product/1085 which will talk to the Raspberry via I2C.
Check out Teensy at https://www.pjrc.com/teensy/ which are Arduino compatible in terms of software but have much more muscle power and IO than any of the ardunio boards.  It also has a teensy footprint.  I used Teensy 3.2 for the compass project.  You should look at Teensy 3.5 or 3.6.  Both have 6 serial IO pins, 3 SPI pins, 3 I2C pins, and gobbs of analog pins.  If you use the multiplexers listed above you can expand your IO capacity by factors.  The 3.5 is 120mhz and 5v tolerant, the 3.6 is 180mhz but strictly 3.3v. 
In terms of the sensor, I considered it but it's only a 25% measurement and has about a 2% error full scale.  That still puts it within acceptable use but doesn't provide much overhead on the top end.  It is however price compatible with typical gas sensors and has a much longer expected life of 5 years.
Maybe I'll buy one anyway just to try it out.
Jon

    On Thursday, August 8, 2019, 12:03:54 AM EDT, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Hi Jon,I was a bit bamboozled by one products description of code for data transmission& thought it would be easier to just have a voltage or an amperage range todeal with. I don't need the temperature & pressure data as I have other sensorsfor that. The arduino uno B I have has only one tx rx option; however you promptedme to review things & found that the arduino mega has 3 tx rx ports & so would do for my 3 sensors. Still considering my options.I am looking to use the arduino & raspberry pi but have been going round in circlesa bit. Was learning to program the arduino, then decided no, I need to use theraspberry Pi, so was learning Python for programming that. Now I have found outthat the raspberry Pi doesn't have any analog pins & has a small maximumcurrent draw. Is there an alternative to those two that is a bit more robust?Alan 
On 8/08/2019, at 2:28 PM, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 CO2 meter has an RS485b analog model.  But I'm curious, why use voltage instead of serial?
Jon

    On Wednesday, August 7, 2019, 09:45:45 PM EDT, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Hi,I've been reading a bit about the solid state optical oxygen sensors whichhave a longer life & are more reliable than traditional galvanic cel ( battery)type O2 sensors. Poseidon developed them for the dive industry & they were hailed as a breakthrough at the time. There is a company, SST sensing that is marketing them for varying applications....https://www.sstsensing.com/optical-oxygen-sensors-key-benefits-and-applications/Is any one familiar with them? There seems to be a big price difference betweenvarying brands.The ones I've seen are calibrated internally for pressure & temperature & transmit data rather than a voltage or current reading. I am looking for a cheap option that has a current or voltage signal rather than data & I will be using something like a raspberry Pi or Arduino to process the reading.I am also wanting 3 as in a rebreather to compare readings.Do they need much of an O2 flow over them or are they ok just being placed randomly within the hull?Cheers Alan<image1.jpeg>_______________________________________________
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